This application proposes to continue the evaluation of retinal function, structure and biochemistry in the cat while manipulating dietary variables of taurine, vitamin A, vitamin E and zinc. The objectives are to determine whether taurine is an essential amino acid for the cat and the nature of turnover of taurine pools, particularly that in the retina, using S35 taurine. In addition, vitamin A deficiency will be studied in this cone-rod retina in the taurine adequate cat to explore the functional (ERG) and structural (EM) characteristics of this degeneration and regeneration with emphasis on differences between rods and cones. This will be compared with taurine deficiency to provide insight on metabolic aspects of cone-rod function. Vitamin E deficiency will be induced and the anticipated macular degeneration carefully evaluated by ERG and EM, and zinc deficiency will be explored for its possible influence on alcohol dehydrogenase activity in the retina which might be expected to affect the production of retinaldehyde and rhodopsin.